(Adapted from the applicant's abstract) Gene therapy of human diseases is accelerating, with many applications in genetic disease, cancer, and infectious disease such as AIDS. The hematopoietic system represents a particularly attractive target for gene therapy due to the ability to isolate, propagate, and genetically modify hematopoietic stem cells (HSC) and other hematopoietic cells in vitro and return them to patients via bone marrow transplantation. However, results of human gene therapy in general and those directed at the hematopoietic system in particular have been inadequate. Significant improvements are needed in the efficiency of gene transfer to HSC, and in the stable expression of foreign genes in HSC and their differentiated progeny after transfer. The long-term goal of this proposal is to develop new systems to facilitate gene therapy of human hematopoietic disease. We will develop a new set of vectors suitable for gene transfer into hematopoietic cells, based upon two different viruses: the human retrovirus HIV-1, and the parvovirus adeno-associated virus (AAV). Based on the recognition that certain gene expression elements may be species-specific and that HIV-1 can infect certain non-cycling cells, we will evaluate the potential for vectors based on the human lentivirus HIV-1 for high-level gene expression in hematopoietic cells. We will also develop a new vector system based on AAV for hematopoietic cell transduction, taking advantage of infection properties and exogenous promoters for gene expression possible with this vector. The different vectors will be formulated with reporter genes for optimization of gene transfer into murine and human HSC, with genes for correction of mouse models of human hematopoietic disease, and for marking, competitive repopulation, and eventual therapeutic correction of human patients, in collaboration with other projects within this grant.